Manufacturing method for liquid crystal display device

ABSTRACT

A LCD device having a large pixel holding capacitance includes opposedly facing first and second substrates, and liquid crystal between them. The first substrate includes a video signal line, a pixel electrode, a thin film transistor having a first electrode connected to the video signal line and a second electrode connected to the pixel electrode, a first silicon nitride film formed above the second electrode, an organic insulation film above the first silicon nitride film, a capacitance electrode above the organic insulation film, and a second silicon nitride film above the capacitance electrode and below the pixel electrode. A contact hole etched in both the first and second silicon nitride films connects the second electrode and the pixel electrode to each other. A holding capacitance is formed by the pixel electrode, the second silicon nitride film and the capacitance electrode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No.13/946,700, filed Jul. 19, 2013, which is a Continuation of U.S.application Ser. No. 13/568,672, filed Aug. 7, 2012, which is aContinuation of U.S. application Ser. No. 13/067,281, filed May 20,2011, which is a Continuation of U.S. application Ser. No. 12/662,961,filed May 13, 2010, which is a Continuation of U.S. application Ser. No.11/802,385, filed May 22, 2007. Priority is claimed based on U.S.application Ser. No. 13/946,700, filed Jul. 19, 2013, which claims thepriority of U.S. application Ser. No. 13/568,672, filed Aug. 7, 2012,which claims the priority of U.S. application Ser. No. 13/067,281, filedMay 20, 2011, which claims the priority of U.S. application Ser. No.12/662,961, filed on May 13, 2010, which claims the priority of U.S.application Ser. No. 11/802,385 filed May 22, 2007, which claims thepriority date of Japanese Patent Japanese application 2006-160428, filedon Jun. 9, 2006, the content of which is hereby incorporated byreference into this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display device, andmore particularly to a technique which is effectively applicable to aliquid crystal display device which includes a silicon nitride film.

2. Description of Related Art

An active matrix liquid crystal display device forms a holdingcapacitance in the inside of a pixel for holding a video signal writtenin the pixel for a relatively long time.

The inventors of the present invention filed a patent application (seefollowing patent document 1) on one method for forming such a holdingcapacitance.

FIG. 7 is a cross-sectional view of an essential part showing oneexample of the holding capacitance described in patent document 1.

As shown in FIG. 7, in an IPS (In-Plane Switching) type liquid crystaldisplay device described in patent document 1, an interlayer insulationfilm IN2 and an organic insulation film PAS are formed to cover a sourceelectrode SD2 of a thin film transistor in order from below. A contacthole CH3A is formed in the interlayer insulation film IN2 and theorganic insulation film PAS in a penetrating manner. A counter electrodeCT and a reflection film RAL are formed on the organic insulation filmPAS in order from below. Further, an interlayer insulation film IN3A isformed to cover the organic insulation film PAS, the counter electrodeCT and the reflection film RAL. The interlayer insulation film IN3A is acoated insulation film or an insulation film formed by a CVD method andis formed also in the inside of the contact hole CH3A. Further, in theinterlayer insulation film IN3A, a contact hole CH3B is formed moreinside than the contact hole CH3A. A pixel electrode PX is formed on theinterlayer insulation film IN3A. Further, the pixel electrode PX isconnected with the source electrode SD2 of the thin film transistor viathe contact hole CH3B and a video signal is applied to the pixelelectrode PX via the thin film transistor. Liquid crystal not shown inthe drawing is driven by an electric field generated between the pixelelectrode PX and the counter electrode CT thus performing a display ofan image.

Here, the holding capacitance is formed by the counter electrode CT(including the reflection film RAL), the interlayer insulation film IN3Aand the pixel electrode PX.

-   Patent Document 1: Japanese patent application no. 2005-312165

SUMMARY OF THE INVENTION

However, in the liquid crystal display device shown in FIG. 7, when thecoated insulation film is used as the interlayer insulation film IN3A,the interlayer insulation film IN3A exhibits a dielectric constant whichis not so high thus giving rise to a drawback that the holdingcapacitance cannot be increased.

Further, although patent document 1 describes a technique which formsthe interlayer insulation film IN3A by the CVD method in place of thecoated insulation film, patent document 1 fails to describe a materialof the film.

Further, FIG. 7 shows the structure which exposes the source electrodeSD2 through the contact hole CH3A in forming the reflection film RAL bypatterning. Accordingly, there exists a possibility that the sourceelectrode SD2 is damaged by etching which is performed for patterningthe reflection film. RAL using an etchant or an etching gas.

Drawbacks other than the above-mentioned drawbacks will become apparentfrom the description of the whole specification or drawings.

In the present invention, as an interlayer insulation film above anorganic insulation film, a silicon nitride film which is formed at a lowtemperature is used. Further, in forming a contact hole in theinterlayer insulation film formed of the silicon nitride film, it isdesirable to collectively etch the interlayer insulation film togetherwith other interlayer insulation film arranged below the interlayerinsulation film.

The present invention may adopt the following constitutions, forexample.

(1) A liquid crystal display device including a first substrateincluding a video signal line, a pixel electrode, a thin film transistorhaving a first electrode thereof connected to the video signal line anda second electrode thereof connected to the pixel electrode, a firstsilicon nitride film formed above the second electrode, an organicinsulation film formed above the first silicon nitride film, acapacitance electrode formed above the organic insulation film, and asecond silicon nitride film formed above the capacitance electrode andbelow the pixel electrode, a second substrate arranged to face the firstsubstrate in an opposed manner, and liquid crystal sandwiched betweenthe first substrate and the second substrate, wherein the second siliconnitride film is a film which is formed at a temperature lower than aforming temperature of the first silicon nitride film, the first siliconnitride film and the second silicon nitride film form a contact holetherein by etching both of the first silicon nitride film and the secondsilicon nitride film collectively by dry etching, the second electrodeand the pixel electrode are connected to each other via the contacthole, a potential different from a potential applied to the pixelelectrode is applied to the capacitance electrode, and a holdingcapacitance is formed by the pixel electrode, the second silicon nitridefilm and the capacitance electrode.

(2) In the constitution (1), the capacitance electrode may have at leasta portion thereof formed of a reflection film.

(3) In the constitution (2), the second electrode may be made of amaterial which is etched by an etchant or an etching gas used inpatterning the reflection film.

(4) In the constitution (2) or (3), the second electrode may include thesame material as the reflection film.

(5) In any one of the constitutions (2) to (4), the organic insulationfilm may have a surface unevenness on a portion thereof corresponding tothe reflection film, and the reflection film may have a surfaceunevenness which reflects the surface unevenness of the organicinsulation film.

(6) In the constitution (5), a height of the surface unevenness of theorganic insulation film between a crest and a valley may be 0.3 μm orless.

(7) In any one of the constitutions (1) to (6), in the contact hole, alower surface of the second silicon nitride film may be brought intocontact with an upper surface of the first silicon nitride film at leastat one portion of the first silicon nitride film.

(8) In any one of the constitutions (1) to (7), in the contact hole, alower surface of the second silicon nitride film may be brought intocontact with an upper surface of the first silicon nitride film over thewhole circumference of the contact hole.

(9) In any one of the constitutions (1) to (8), in the contact hole, anend portion of a lower surface of the second silicon nitride film may besubstantially aligned with an end portion of an upper surface of thefirst silicon nitride film.

(10) In any one of the constitutions (1) to (8), in the contact hole, anend portion of a lower surface of the second silicon nitride film may beretracted from an end portion of an upper surface of the first siliconnitride film.

(11) In any one of the constitutions (1) to (10), in the contact hole,the organic insulation film may not be exposed from the second siliconnitride film.

(12) In any one of the constitutions (1) to (11), the capacitanceelectrode may have at least a portion thereof formed of a transparentconductive film.

(13) In any one of the constitutions (1) to (12), the pixel electrodesmay be formed of a transparent conductive film.

(14) In any one of the constitutions (1) to (13), the second siliconnitride film may be formed of a film which exhibits an etching rate inthe vicinity of a surface thereof faster than the etching rate in otherportion thereof.

(15) In the constitution (14), a film thickness of a portion of thesecond silicon nitride film arranged in the vicinity of the surface ofthe second silicon nitride film which exhibits the etching rate fasterthan the etching rate of other portion of the second silicon nitridefilm may be set to a value not less than 5% and not more than 30% of afilm thickness of the second silicon nitride film.

(16) In any one of the constitutions (1) to (15), the second siliconnitride film may be a film formed by a plasma CVD method.

(17) In any one of the constitutions (1) to (16), the capacitanceelectrode may also function as a counter electrode and the liquidcrystal may be driven by an electric field generated between the pixelelectrode and the counter electrode.

(18) In any one of the constitutions (1) to (16), the second substratemay include a counter electrode and the liquid crystal may be driven byan electric field generated between the pixel electrode and the counterelectrode.

(19) A liquid crystal display device including a first substrateincluding a video signal line, a pixel electrode, a thin film transistorhaving a first electrode thereof connected to the video signal line anda second electrode thereof connected to the pixel electrode, an organicinsulation film formed above the second electrode, a capacitanceelectrode formed above the organic insulation film, and a siliconnitride film formed above the capacitance electrode and below the pixelelectrode, a second substrate arranged to face the first substrate in anopposed manner, and liquid crystal sandwiched between the firstsubstrate and the second substrate, wherein the silicon nitride film isa film which is formed at a temperature lower than a heat-resistanttemperature of the organic insulation film after the formation of theorganic insulation film, and a potential different from a potentialapplied to the pixel electrode is applied to the capacitance electrode,and a holding capacitance is formed by the pixel electrode, the siliconnitride film and the capacitance electrode.

(20) In the constitution (19), the silicon nitride film may be a filmformed by a plasma CVD method.

(21) A liquid crystal display device including a first substrateincluding a video signal line, a pixel electrode, a thin film transistorhaving a first electrode thereof connected to the video signal line anda second electrode thereof connected to the pixel electrode, an organicinsulation film formed above the thin film transistor, a reflection filmformed above the organic insulation film, a silicon nitride film formedabove the reflection film and below the pixel electrode, a secondsubstrate arranged to face the first substrate in an opposed manner, andliquid crystal sandwiched between the first substrate and the secondsubstrate, wherein the organic insulation film has a surface unevennesson a portion thereof corresponding to the reflection film, thereflection film has a surface unevenness which reflects the surfaceunevenness of the organic insulation film, the silicon nitride film isformed at a temperature lower than a heat-resistant temperature of theorganic insulation film after the formation of the organic insulationfilm, and a height of the surface unevenness of the organic insulationfilm between a crest and a valley is 0.3 μm or less.

(22) In the constitution (21), the silicon nitride film may be a filmformed by a plasma CVD method.

Here, the above-mentioned constitutions are exemplified only as examplesand the present invention can be suitably modified without departingfrom a technical concept of the present invention. Further, examples ofthe constitution of the present invention besides the above-mentionedconstitutions will become apparent from the description of the wholespecification or drawings.

To explain typical advantageous effects of the present invention, theyare as follows.

According to the present invention, it is possible to form a holdingcapacitance which exhibits a large capacitance.

Further, the present invention can prevent damages from being applied tothe source electrode.

Further, according to the present invention, the process can besimplified.

Further, according to the present invention, it is possible to ensurethe electric connection in the contact hole.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view for explaining a liquid crystal display device of anembodiment 1 of the present invention and also is a cross-sectional viewtaken along a line A-A′ in FIG. 2;

FIG. 2 is a plan view for explaining the liquid crystal display deviceof the embodiment 1 of the present invention;

FIG. 3 is a view for explaining the liquid crystal display device of theembodiment 1 of the present invention, and also is a cross-sectionalview taken along a line B-B′ in FIG. 2;

FIG. 4A to FIG. 4F are views for explaining a manufacturing method ofthe liquid crystal display device of the embodiment 1 of the presentinvention;

FIG. 5 is a view for explaining a liquid crystal display device of anembodiment 2 of the present invention, and also is a view whichcorresponds to FIG. 1;

FIG. 6A to FIG. 6C are views for explaining a liquid crystal displaydevice of an embodiment 3 of the present invention, and also arecross-sectional views showing a contact hole portion in an enlargedmanner; and

FIG. 7 is a cross-sectional view of an essential part of a liquidcrystal display device for showing one example of a holding capacitancedescribed in patent document 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention are explained in conjunction withdrawings.

Embodiment 1

In an embodiment 1, the explanation is made with respect to one examplein which the present invention is applied to an IPS liquid crystaldisplay device.

FIG. 1 is a view for explaining a liquid crystal display device of theembodiment 1 of the present invention and also is a cross-sectional viewtaken along a line A-A′ in FIG. 2. FIG. 2 is a plan view for explainingthe liquid crystal display device of the embodiment 1 of the presentinvention. FIG. 3 is a view for explaining the liquid crystal displaydevice of the embodiment 1 of the present invention and also is across-sectional view taken along a line B-B′ in FIG. 2.

As shown in FIG. 1 to FIG. 3, liquid crystal LC is sandwiched between atransparent insulation substrate (first substrate) SUB1 made of a glassor the like and a transparent insulation counter substrate (secondsubstrate) SUB2 made of a glass or the like.

The liquid crystal display device according to the present invention isan active matrix type liquid crystal display device in which a pluralityof pixels are arranged in a matrix array. The substrate SUB1 includes aplurality of scanning signal lines GL and a plurality of video signallines DL which intersect the plurality of scanning signal lines GL. Inthe vicinity of each intersection, a thin film transistor is arranged asa switching element of the pixel. In FIG. 2, one pixel out of aplurality of pixels which are arranged in a matrix array is shown.

On the substrate SUB1, in order from below, a base film UC, asemiconductor film PS made of poly-silicon or the like, a gateinsulation film. GI, gate electrodes GT of the thin film transistors,and an interlayer insulation film IN1 are formed. On the interlayerinsulation film IN1, drain electrodes (first electrodes) SD1 of the thinfilm transistors and source electrodes (second electrodes) SD2 of thethin film transistors are formed. Here, there may be a case that SD1 maybe used to refer to the source electrodes. In such a case, SD2 may beused to refer to the drain electrodes. In this specification, SD1 isused to refer to the drain electrodes.

The gate electrodes GT are integrally formed with the scanning signalline GL. One portion of the video signal line DL also functions as thedrain electrode SD1 thus providing the structure in which the videosignal line DL and the drain electrode SD1 are connected with eachother. The drain electrode SD1 is connected to the drain region of thethin film transistor via the contact hole CH1 which is formed in thegate insulation film GI and the interlayer insulation film IN1. Thesource electrode SD2 is connected to a source region of the thin filmtransistor via a contact hole CH2 formed in the gate insulation film GIand the interlayer insulation film IN1.

On the drain electrodes SD1 and the source electrodes SD2, an interlayerinsulation film IN2 is formed. On the interlayer insulation film IN2, anorganic insulation film PAS is formed. On the organic insulation filmPAS, counter electrodes CT and a reflection film RAL are formed. On thecounter electrodes CT and the reflection film RAL, an interlayerinsulation film IN3 is formed. On the interlayer insulation film IN3,pixel electrodes PX are formed. The pixel electrodes are connected tothe source electrodes SD2 of the thin film transistors via contact holesCH3 which are formed in the interlayer insulation film IN2 and theinterlayer insulation film IN3.

On the pixel electrodes PX, an orientation film ORI1 is formed. Further,on a side of the substrate SUB1 opposite to the liquid crystal LC, apolarizer POL1 is arranged. Here, the orientation film ORI1 and thepolarizing plate POL1 are omitted from FIG. 1.

On the counter substrate SUB2, a black matrix BM, color filters CF, anovercoat film OC, an orientation film ORI2 are formed. Further, apolarizer POL2 is arranged on a side of the counter substrate SUB2opposite to the liquid crystal LC.

A retardation plate or a coated retardation layer may be arranged on atleast one of the substrate SUB1 and the counter substrate SUB2 whennecessary.

In this embodiment, the pixel electrode PX includes a linear portion andis formed into a comb-teeth shape. The counter electrode CT is formed ina planar shape. Here, the liquid crystal LC is driven by an electricfield which is generated between the pixel electrode PX and the counterelectrode CT to perform a display.

The pixel electrode PX and the counter electrode CT are formed of atransparent conductive film such as an ITO film, for example. Thereflection film RAL is formed in one region within one pixel. Due tosuch a constitution, it is possible to perform a transflective(partially transmissive) display which includes a transmissive regionand a reflection region in one pixel. Accordingly, it is possible toperform a transmissive display by making use of light from a backlightnot shown in the drawing under a dark environment, while it is possibleto perform a reflective display by making use of an external light undera bright environment. The reflection film RAL has, for example, thetwo-layered structure which has a lower layer thereof made of molybdenumtungsten alloy (MoW) and an upper layer thereof made of an aluminumsilicon alloy (AlSi) containing 1% of Si, and the reflection film. RALis connected to the counter electrode CT. When it is necessary to changea thickness of the liquid crystal LC in the transmissive region and athickness of the liquid crystal in the reflection region, for example,it is preferable to form a stepped-portion forming layer not shown inthe drawing on the counter substrate SUB2.

A common potential different from a potential applied to the pixelelectrodes PX is applied to the counter electrode CT (and the reflectionfilm RAL). Accordingly, the holding capacitance is formed by the counterelectrode CT (and the reflection film RAL), the pixel electrodes PX andthe interlayer insulation film IN3. That is, the counter electrode CT(and the reflection film RAL) also functions as a capacitance electrode.Here, when a silicon nitride film is used as the interlayer insulationfilm IN3, compared to a case in which a coated insulation film IN3A isused as the interlayer insulation film IN3 which is explained inconjunction with FIG. 7, or a case in which a silicon oxide film is usedas the interlayer insulation film IN3, a high dielectric constant can beobtained. Accordingly, it is possible to increase the holdingcapacitance. Further, by forming the pixel electrodes PX and the counterelectrode CT using a transparent conductive film, it is possible to forma transparent holding capacitance and hence, a numerical aperture at thetime of performing a transmissive display can be increased.

The interlayer insulation film IN2 may preferably be a silicon nitridefilm which is formed by a plasma CVD method. It is desirable that theinterlayer insulation film IN2 is formed at a high temperature to obtaina dense film. The organic insulation film PAS may preferably be formedusing a photosensitive acrylic resin or the like, for example. With theuse of the organic insulation film PAS, it is possible to increase theflatness compared a case in which an inorganic insulation film is usedas the interlayer insulation film IN2. Further, the organic insulationfilm PAS having a large thickness can be easily formed and hence, it ispossible to decrease the parasitic capacitance. Further, by making useof a halftone exposure when necessary, the surface unevenness may bepartially formed on the organic insulation film PAS easily.

The interlayer insulation film IN3 is formed above the organicinsulation film PAS. The organic insulation film PAS generally hascomparatively low heat resistance and hence, in this embodiment, theinterlayer insulation film IN3 is formed by a plasma CVD method at atemperature lower than a forming temperature of the interlayerinsulation film IN2. To make the dielectric constant high, a siliconnitride film is adopted as the interlayer insulation film IN3. Theinterlayer insulation film IN3 is formed at a low temperature and hence,the interlayer insulation film IN3 is not as dense as the interlayerinsulation film IN2. However, due to the provision of the denseinterlayer insulation film IN2, there arises no problem in practical usein the protection of the thin film transistor.

Further, a silicon nitride film is adopted by both of the interlayerinsulation film IN2 and the interlayer insulation film IN3 and hence,both of the interlayer insulation films IN2 and IN3 can be collectivelyetched by dry etching to form the contact hole CH3 therein. Accordingly,it is possible to simplify the processing.

The source electrode SD2 is made of the same material (for example, analuminum silicon alloy or a molybdenum tungsten alloy) as the reflectionfilm RAL. In this case, in the structure explained in conjunction withFIG. 7, the source electrode SD2 is exposed at the time of forming thereflection film RAL and hence, there exists a drawback that the sourceelectrode SD2 may be damaged by an etchant or an etching gas which isused for forming (patterning) the reflection film RAL. On the otherhand, by collectively etching the interlayer insulation film IN2 and theinterlayer insulation film IN3 in the same manner as this embodiment,the source electrode SD2 is covered with the interlayer insulation filmIN2 at the time of forming the reflection film RAL and hence, it ispossible to avoid the above-mentioned problem.

Next, one example of a manufacturing method of the liquid crystaldisplay device of this embodiment is explained. FIG. 4A to FIG. 4F areviews for explaining the manufacturing method of the embodiment 1 of theliquid crystal display device of the present invention. FIG. 4A to FIG.4F illustrate the vicinity of the contact hole CH3 in FIG. 1 in anenlarged manner.

As shown in FIG. 4A, after the thin film transistors are formed by ausual method, a silicon nitride film is formed on the source electrodesSD2 as the interlayer insulation film IN2 using a plasma CVD method.With respect to the forming condition of the interlayer insulation filmIN2 at this time, the forming temperature (substrate temperature) is setto 390° C. and the film thickness of the interlayer insulation film IN2is set to 300 nm.

Thereafter, the organic insulation film PAS is formed, for example, bycoating, exposing and patterning a photosensitive acrylic resin. Athickness of the organic insulation film PAS is set to 2.2 μm.

Next, as shown in FIG. 4B, the counter electrodes CT made of ITO andhaving a film thickness of 77 nm are formed on the organic insulationfilm PAS by patterning. On the counter electrodes CT, the reflectionfilm RAL having the two-layered structure including upper layer made ofan aluminum silicon alloy (AlSi) containing 1% of Si having a thicknessof 150 nm and a lower layer made of a molybdenum tungsten alloy (MoW)having a thickness of 50 nm is formed by patterning. For patterning thereflection film RAL, a mixed acid formed by mixing a phosphoric acid, anitric acid, an acetic acid and ammonium fluoride is used as an etchant.Here, the source electrode SD2 has the three-layered structure includingan upper layer made of a molybdenum tungsten alloy (MoW) having athickness of 75 nm, an intermediate layer made of an aluminum siliconalloy (AlSi) containing 1% of Si and having a thickness of 500 nm and alower layer made of a molybdenum tungsten alloy (MoW) having a thicknessof 40 nm and has the same materials as the materials of the reflectionfilm RAL. However, at this point of time, the source electrode SD2 iscovered with the interlayer insulation film IN2 and hence, there is nopossibility that the source electrode SD2 is damaged.

Here, even when the source electrode SD2 and the reflection film RAL maynot be formed of the same material, when the source electrode SD2 ismade of a material which is etched by the etchant or the etching gasused for patterning the reflection film RAL, there arises similardrawbacks and hence, it is preferable that the source electrode SD2 isnot exposed at the time of forming the reflection film RAL. For example,a case in which the upper layer of the source electrode SD2 is made oftitanium (Ti) or the like may be considered.

Next, as shown in FIG. 4C, a silicon nitride film is formed on thecounter electrodes CT and the reflection film RAL as the interlayerinsulation film IN3 formed by the plasma CVD method. With respect to theforming condition at this point of time, by taking influence exertedupon the organic insulation film PAS arranged below the interlayerinsulation film IN3 into consideration, the interlayer insulation filmIN3 is formed at a temperature lower than the heat-resistant temperatureof the organic insulation film PAS, and the film forming temperature(substrate temperature) is set to 180° C. to 250° C. (preferably 220° C.to 230° C., especially 220° C.), and the film thickness is set to 100 nmto 500 nm (preferably 200 nm to 300 nm, especially 300 nm).

Further, it is desirable to set an etching rate of the vicinity of asurface the interlayer insulation film IN3 faster than an etching rateof other portions (bulk layers) of the interlayer insulation film IN3.This can be obtained by setting a gas flow rate between mono-silane(SiH4) and ammonia (NH3) which are material gasses of the interlayerinsulation film IN3 at the time of forming by a plasma CVD to 1:6 informing a usual bulk layer of the interlayer insulation film IN3 and byincreasing the gas flow rate to 1:16 in the course of the step forforming the interlayer insulation film IN3, for example. It is desirableto set a film thickness of the interlayer insulation film IN3 in thevicinity of the surface of the interlayer insulation film IN3 having theetching rate faster than the etching rate of other portion to a valueequal to or more than 5% and equal to or less than 30% (preferablyapproximately 8% to 12%) of the film thickness of the interlayerinsulation film. IN3. In this manner, by forming the film having thefast etching rate (retracted layer) in the vicinity of the surface ofthe interlayer insulation film IN3, it is possible to form the contacthole CH3 into a normal tapered shape at the time of forming the contacthole CH3.

Next, as shown in FIG. 4D, a resist PR is formed.

Then, as shown in FIG. 4E, using the resist PR as a mask, the interlayerinsulation film IN2 and the interlayer insulation film IN3 arecollectively etched thus forming the contact holes CH3. Using a mixedgas made of sulfur hexafluoride (SF₆) and oxygen (O₂) as an etching gas,the interlayer insulation film IN2 and the interlayer insulation filmIN3 are etched by dry etching. By collectively etching both of theinterlayer insulation film IN2 and the interlayer insulation film IN3,the processing can be simplified.

Thereafter, the resist PR is removed.

Next, as shown in FIG. 4F, the pixel electrodes PX made of ITO areformed on the interlayer insulation film IN3. A film thickness of thepixel electrode PX is set to 77 nm.

Here, in this embodiment, a case in which the interlayer insulation filmIN2 is formed on the drain electrodes SD1 and the source electrodes SD2has been explained. However, depending on a degree of requirement ofreliability or the like, the interlayer insulation film IN2 is not alayer which is always necessary. That is, even when the organicinsulation film PAS is directly formed on the drain electrode SD1 andthe source electrode SD2, such a constitution can obtain theadvantageous effects of the present invention that the holdingcapacitance can be increased. Here, in this case, in place ofeliminating the interlayer insulation film IN2, it is preferable to formthe interlayer insulation film IN1 using a silicon nitride film or astacked film including a silicon nitride film (for example, thetwo-layered structure formed of a silicon oxide film and the siliconnitride film).

Further, in forming the interlayer insulation film IN2, in thisembodiment, the explanation has been made with respect to the case inwhich the interlayer insulation film IN2 is formed of the siliconnitride film. However, the constitution is not limited to such a caseand the interlayer insulation film IN2 may be formed of a silicon oxidefilm. Here, also in this case, it is preferable that the interlayerinsulation film IN1 is formed of a silicon nitride film or a stackedfilm including a silicon nitride film (for example, the two-layeredstructure formed of the silicon oxide film and the silicon nitridefilm).

Embodiment 2

In the embodiment 2, one example in which the formation of a surfaceunevenness to perform a diffusion reflection is applied to theconstitution of the embodiment 1 is explained. FIG. 5 is a view forexplaining the embodiment 2 of the liquid crystal display deviceaccording to the present invention, and also is a view corresponding toFIG. 1. Here, in this embodiment and succeeding embodiments which followthe embodiment 2, points makes these embodiments different from theembodiment 1 are mainly explained and the explanation of contents commonwith the contents of the embodiment 1 is omitted.

The constitution which makes the embodiment 2 different from theconstitution of the embodiment 1 lies in that the surface unevenness(projections PJ) is formed on a portion of the organic insulation filmPAS corresponding to the reflection film RAL by making use of a halftoneexposure, for example, and the reflection film RAL has an uneven surfaceshape by reflecting the surface unevenness of the organic insulationfilm PAS. Due to such a constitution, it is possible to perform adiffusion reflection in the reflection display and hence, a displayquality is enhanced.

The organic insulation film PAS is used for forming the surfaceunevenness and hence, it is possible to easily form the surfaceunevenness compared to a case in which the surface unevenness is formedan inorganic insulation film.

However, when the interlayer insulation film IN3 is used of a filmformed by the plasma CVD method, it is not possible to sufficientlylevel the surface unevenness and hence, the surface unevenness is alsoreflected on the pixel electrodes PX. To decrease the influence of thesurface unevenness on the display quality, it is preferable to set aheight of the surface unevenness between a crest and a valley of theorganic insulation film PAS to a value equal to or less than 0.3 μm(more preferably, equal to or less than 0.2 μm). Here, to obtain afunction of diffusion reflection, it is preferable to set the height ofthe surface unevenness between a crest and a valley to a value equal toor more than 0.1 μm.

Embodiment 3

The embodiment 3 describes a modification of a shape of the contact holeCH3 of the present invention.

FIG. 6A to FIG. 6C are views for explaining the embodiment 3 of thepresent invention, and also are cross-sectional views showing thecontact hole portion in an enlarged manner.

As shown in FIG. 6A and FIG. 6B, in the contact hole CH3, it isdesirable that an organic insulation film PAS is not exposed from aninterlayer insulation film IN3. That is, in the contact hole CH3, it isdesirable that a lower surface of the interlayer insulation film IN3 isbrought into contact with an upper surface of an interlayer insulationfilm IN2 over the whole circumference.

As shown in FIG. 6C, at an exposed portion EX where the organicinsulation film PAS is exposed from the interlayer insulation film IN3,a pixel electrode PX formed on the interlayer insulation film IN3 maypossess a high resistance or is liable to be easily disconnected. Suchan exposed portion PX is formed due to the following reason.

In a stage before etching the interlayer insulation film IN3 by dryetching, at a portion of an inclined surface of the organic insulationfilm PAS, the interlayer insulation film IN3 per se forms an inclinedsurface which is inclined with respect to a substrate SUB1. When the dryetching is performed, the interlayer insulation film IN3 is etched witha predetermined taper angel and this angle assumes a fixed angle withrespect to an upper surface of the interlayer insulation film IN3.Accordingly, an etched end surface of the interlayer insulation film IN3positioned on the inclined surface as shown in FIG. 6C increases anangle measured using a main surface of the substrate SUB1 as thereference compared to a case in which the interlayer insulation film IN3is formed on a horizontal surface as shown in FIG. 6A and FIG. 6B.Further, depending on a case, the etched end surface may take a reversetapered state as shown in FIG. 6C. Due to such a reason, a shape whichgenerates the exposed portion EX is formed.

Here, in FIG. 6C, although the exposed portion EX is formed on a leftside of the cross-sectional view of the contact hole CH3, the organicinsulation film PAS is not exposed from the interlayer insulation film.IN3 on a right side of the cross-sectional view. Such a structure isbrought about by the misalignment of the resist PR explained inconjunction with FIG. 4D. When at least one connection path where theexposed portion EX is not present is ensured, although the resistancemay be increased, the electrical connection can be established andhence, such a shape may be adopted provided that there arises no problemin display. The shape can be realized by bringing a lower surface of theinterlayer insulation film IN3 into contact with an upper surface of theinterlayer insulation film IN2 at least one portion of the contact holeCH3.

In FIG. 6A, an end portion of the lower surface of the interlayerinsulation film IN3 and an end portion of the upper surface of theinterlayer insulation film IN2 substantially agree with each other. Thatis, a taper of the interlayer insulation film IN3 and a taper of theinterlayer insulation film IN2 are contiguously formed.

In FIG. 6B, the end portion of the lower surface of the interlayerinsulation film IN3 is retracted from the end portion of the uppersurface of the interlayer insulation film IN2 by a distance d. Due tosuch a constitution, a stepped portion can be made small and hence, thepossibility of the occurrence of disconnection of the pixel electrode PXcan be reduced and, at the same time, a thickness of the pixel electrodePX in a film shape can be decreased. By increasing an etching rate ofthe interlayer insulation film IN3 compared to an etching rate adoptedby the structure shown in FIG. 6A, such a shape can be realized.

Embodiment 4

This embodiment 4 is directed to a case in which the present inventionis applied to a transmissive liquid crystal display device.

Here, the formation of the reflection film RAL in the embodiment 1 maybe omitted.

Further, in this case, a portion of the contact hole CH3 may beconfigured such that, in place of the structure explained in conjunctionwith FIG. 1, as explained in conjunction with FIG. 7, the contact holeCH3A is preliminarily formed in the interlayer insulation film IN2 and,thereafter, the contact hole CH3B may be formed in the interlayerinsulation film IN3A. Also in such a case, it is possible to obtain anadvantageous effect that the holding capacitance can be increased byusing the silicon nitride film as the interlayer insulation film IN3.

This embodiment may also adopt the shape of the contact hole explainedin conjunction with the embodiment 3.

Embodiment 5

This embodiment 5 explains a case in which the present invention isapplied to a vertical electric field liquid crystal display device inplace of the IPS liquid crystal display device explained in conjunctionwith the embodiment 1.

In the vertical electric field liquid crystal display device, a counterelectrode not shown in the drawing may be formed on the countersubstrate SUB2 side. Due to such a constitution, the liquid crystaldisplay device can perform a display by driving liquid crystal LC usingan electric field generated between pixel electrode PX on the substrateSUB1 side and the counter electrode not shown in the drawing on thecounter electrode SUB2 side. Here, the pixel electrodes PX may be formedin a planar shape instead of a comb-teeth-shape shown in FIG. 2.

In the vertical electric field liquid crystal display device of thisembodiment, the counter electrode CT (and the reflection film RAL) shownin FIG. 1 functions as capacitive electrode instead of counterelectrode.

Here, this embodiment may be combined with the embodiment 2 to performthe diffusion reflection.

Further, this embodiment may adopt the shape of the contact hole shownin the embodiment 3.

Further, a transmissive liquid crystal display device may be constitutedby combining this embodiment with the embodiment 4.

Here, the constitutions which have been explained in conjunction withthe respective embodiments heretofore merely constitute examples andvarious modifications can be properly made without departing from atechnical concept of the present invention.

What is claimed is:
 1. A display device comprising: a first substrate including a video signal line, a first electrode, a second electrode, a thin film transistor having a third electrode thereof connected to the video signal line and a fourth electrode thereof connected to the first electrode, a first inorganic insulation film formed above the fourth electrode, an organic insulation film formed above the first inorganic insulation film, a second substrate arranged to face the first substrate in an opposed manner, wherein the second electrode is formed above the organic insulation film, a second inorganic insulation film is formed above the second electrode and below the first electrode, the organic insulation film has a first contact hole, the first inorganic insulation film has a second contact hole, and the second inorganic insulation film has a third contact hole, the first electrode is electrically coupled to the fourth electrode via the first contact hole, the second contact hole, and the third contact hole, the first inorganic insulation film has an upper surface which faces the second substrate, the second inorganic insulation film has a lower surface which faces the first substrate, at least a part of the lower surface faces the upper surface without the organic insulation film therebetween.
 2. A display device according to claim 1, wherein the part of the lower surface faces the upper surface above the fourth electrode.
 3. A display device according to claim 1, wherein the part of the lower surface faces the upper surface over the whole circumference of the first contact hole.
 4. A display device according to claim 1, wherein the second inorganic insulation film does not exist in the second contact hole.
 5. A display device according to claim 4, wherein the second inorganic insulation film is not contact with a side wall of the second contact hole.
 6. A display device according to claim 1, wherein an end portion of the lower surface is substantially aligned with an end portion of the upper surface.
 7. A display device according to claim 1, wherein an end portion of the lower surface is retracted from an end portion of the upper surface.
 8. A display device according to claim 1, wherein the first inorganic insulation film is formed of a first silicon nitride film and the second inorganic insulation film is formed of a second silicon nitride film.
 9. A display device according to claim 8, wherein the first silicon nitride film is more dense than the second silicon nitride film.
 10. A display device according to claim 8, wherein the first silicon nitride film has higher crystallinity than the second silicon nitride film.
 11. A display device according to claim 8, wherein a molecular density of the first silicon nitride film is larger than a molecular density of the second silicon nitride film.
 12. A display device according to claim 1, wherein the second inorganic insulation film is not in contact with the fourth electrode.
 13. A display device according to claim 1, wherein the display device further comprises a plurality of pixels, each of the pixels having a pixel electrode, the first electrode is the pixel electrode.
 14. A display device according to claim 13, wherein the second electrode is a counter electrode.
 15. A display device according to claim 1, wherein a potential different from a potential applied to the first electrode is applied to the second electrode, a holding capacitance is formed by the first electrode, the second inorganic insulation film and the second electrode.
 16. A display device according to claim 1, wherein the first contact hole has a side wall which consists of the organic insulation film, and at least a part of the side wall is in contact with the second inorganic insulation film. 